Enable showing line numbers, which makes it easier to find
the correct place in long files. Due to the "tiny" build,
the functionality is only available from cmdline with "-l"
option.
For example: nano -l /etc/banner
Key shortcut M-n is disabled due to "tiny".
See https://savannah.gnu.org/bugs/?61441 for explanation.
Also
* remove without-slang config option, deprecated in Dec 2020
* adopt AUTORELEASE
Signed-off-by: Hannu Nyman <hannu.nyman@iki.fi>